1. Field of the Invention
This invention relates to a photoprocessing apparatus for the processing of semiconductors and thin films, and particularly to a photoprocessing apparatus which is useful for large-area batch processing of a large number of substrates.
2. Description of the Related Art
Recently there has been increased interest in the photoprocessing of semiconductors and thin films. The term photoprocessing includes photo-deposition, photo-etching, photo-lithography, etc. With the recent advances in laser and incoherent radiation processing (i.e., photoprocessing) of semiconductors, a need has arisen for an apparatus which is capable of large-area batch processing.
Photo-deposition techniques have attracted attention because of the increased degree of control which is made possible through the use of photo-deposition. Photo-deposition is the deposit of a material on a substrate as a result of a reaction between a molecule and electromagnetic radiation. For example, photo-deposition of a material on a wafer can be caused by placing a wafer in a chamber and pumping a reaction gas which includes the material to be deposited, into the chamber. Then, a light source is employed to excite the reaction gas, causing the gas molecule to be blown apart. That is, the desired material for deposit is dissociated from the gas molecule (photo-dissociation) and deposited on the wafer. Photo-deposition is a chemical process which requires that the wavelength and intensity (i.e., power) of the electromagnetic beam be selected so as to match with the gas molecule from which the desired material is to be deposited. The chemical reaction is activated by light, and the reaction may be aided by heating the chamber in which the substrate is placed, to a temperature of from room temperature to 1000.degree. C. The use of photo-deposition techniques is particularly advantageous because a better quality film (from an impurity standpoint) can be obtained at a lower temperature than with other types of processing such as standard chemical vapor deposition, sputtering or liquid phase expitaxy. In addition, photo-deposition is particularly advantageous because temperatures in the range of 300.degree. to 400.degree. C. or lower can be employed, thereby making high quality deposition possible on those substrates which are damaged at higher temperatures (e.g., GaAs and InP).
In the past, lenses (particularly large telescopic lenses including a telescope with cylindrical lenses) or cassegranian beam expanders have been employed to expand the light source for photo-deposition. However, the large telescopic lenses become prohibitively expensive at ultraviolet wavelengths, and the cassegranian beam expanders create a donut shaped beam which is not particularly suitable for the photo-deposition process. In addition, both the lenses and the cassegranian beam expanders are capable of only low processing throughput.
One of the primary roadblocks to the commercial use of the photo-deposition process is the development of a technique for mass production of wafers using the photo-deposition process. Thus, there remains a need in the photoprocessing art for a technique for carrying out mass production of wafers using photoprocessing.